1. Field of the Invention
The present invention relates to a method for setting determination conditions used for determining whether a molded product is non-defective or defective.
2. Description of the Relevant Art
Generally, in production of molded products by use of an injection molding machine, conditions for determining whether a molded product is non-defective or defective (hereinafter referred to as a “determination condition”) are set in advance, and whether a molded product is non-defective or defective is determined by use of the determination condition.
Conventionally, in many cases such a determination condition has been automatically set. In the case of such an automatic setting, molding data are collected during a predetermined number of shots in an early stage; a center value is obtained from the collected molding data, and a monitor range (non-defective range) is set in such a manner that the monitor range extends by a predetermined amount upward and downward from the center value. For example, in a method for automatically setting a reference value used for non-defective/defective determination of molded products disclosed in Japanese Patent Application Laid-Open (kokai) No. 2(1990)-106315, variable data for determining whether a molded product is non-defective or defective are detected during each molding cycle; and the detected variable data are compared with reference values set for the variable in order to determine whether the molded product is non-defective or defective. The reference values for the variable are automatically set in such a manner that the injection molding machine is operated in a reference value setting mode in order to detect variable data in each molding cycle; and the maximum and minimum values of the detected variable data are set as the reference values of the variable. Further, in a product non-defective/defective determination method for an injection molding machine disclosed in Japanese Patent Application Laid-Open (kokai) No. 2002-79560, determination as to whether a molded product is non-defective or defective is performed statistically, as follows. A molding condition determining process is performed so as to find molding conditions which enable stable molding of non-defective products, through a total of N shots. Subsequently, with regard to at least one actual value obtained in each shot, for each shot starting from an (N+1)-th shot, an average value and a standard deviation are calculated from actual value data of the past N shots immediately before the (N+1)-th shot, an initial multiplying factor ki is set for the calculated standard deviation, and for each shot a determination is made as to whether the actual value satisfies the relation (average value−ki×standard deviation)≦actual value≦(average value+ki×standard deviation). When the above relation is satisfied, a molded product is judged to be non-defective, and when the above relation is not satisfied, a molded product is judged to be defective. While the above determination is performed repeatedly, an optimal multiplying factor ko is set for the standard deviation. After that, the optimal multiplying factor ko is set for the standard deviation calculated for each shot, and for each shot a determination is made as to whether the actual value satisfies the relation (average value−ko×standard deviation)≦actual value≦(average value+ko×standard deviation). When the above relation is satisfied, a molded product is judged to be non-defective, and when the above relation is not satisfied, a molded product is judged to be defective. Furthermore, a method for automatically setting upper and lower limits of molding conditions of a molding machine disclosed in Japanese patent No. 2545465 uses a control apparatus using a micro computer for driving and controlling respective portions of the molding machine on the basis of various preset molding operation condition values and measurement information from various sensors. In order to determine quality of molded product during a continuous automatic operation, the control apparatus not only has a function for comparing an actual value of a predetermined monitor item with upper and lower limits thereof, and determining whether a molded product is non-defective or defective, on the basis of the comparison results, but also has a function for automatically setting the upper and lower limits. Specifically, when a predetermined number of initial shots have been completed after start of the continuous automatic operation, an actual value x of each monitor item is measured every time a predetermined number of shots are performed, and for each monitor item at least a variation range R of the actual value×(R=xmax−xmin) and an intermediate value Mi of the actual value x (Mi=xmin+(R/2)) are statistically calculated. On the basis of the results of this calculation, upper and lower limits for each monitor item are automatically determined in such a manner that the upper and lower limits are separated from the intermediate value Mi by equal amounts.
Incidentally, when a determination condition is set for products which are not required to have very high quality, the determination condition is preferably set by use of molding data of non-defective products having some degree of variation, rather than molding data of the best quality products, because use of such a determination condition increases yield and enables efficient production.
However, the conventional methods for automatically setting determination conditions fail to consider collecting only molding data which are desirable for setting determination conditions, and simply collects molding data after data values have become stable. Therefore, the conventional methods encounter difficulty in setting appropriate determination conditions, and take time for fine adjustment, resulting in an increase in man-hours involved in setting work, thereby hindering enjoyment of the merits of automation.